The movement of a motor vehicle involves providing enough power to overcome, at least in part, aerodynamic drag. The efficiency of the shape of a vehicle in minimizing aerodynamic drag is referred to as drag coefficient. In general, drag can be minimized by promoting and maintaining laminar flow over the surface of the vehicle body. It is widely recognized that a ‘perfect’ vehicle body shape in terms of drag efficiency is a teardrop shape. Such a shape, however, poses other issues related to vehicle packaging, practicality and marketability. Modern production car designs have progressed significantly from early, chunky vehicle designs by making substantial improvements to the aerodynamic efficiency of the front two-thirds of the vehicle, i.e. to about the maximum cross sectional point of the vehicle. The demand, however, for a usable trunk space and rear indicator lighting in a typical vehicle dictate a generally truncated rear end, which results in turbulence. Turbulence behind the rear end of a moving vehicle is a major source of drag.
Typically, fixed wing elements or “spoilers” are used in an attempt to control the turbulence and also provide down force to improve rear wheel traction. The effectiveness of fixed spoilers is limited, however, at normal city or highway speeds. Accordingly, it remains desirable to provide an aerodynamic control element that improves over conventional designs by specifically addressing the need to minimize drag due to turbulence behind the rear end of the vehicle.